By Andrew Scogings, IM
Correspondent, and Rob Barnett *
Thessally Resources Pty Ltd is a privately-owned Australian
company that is focused on industrial minerals exploration
and development opportunities. Thessally owns exploration
licences in the Rum Jungle Mineral Field in the Northern
Territory, Australia, which contains high-grade
macrocrystalline magnesite discovered by BHP in the
late-1970s.
One of the exploration licences (EL
27724) covers an area of magnesium mineralisation which is
locally called the Huandot Magnesite Deposit and which has been
estimated to contain a mineral resource of 4.6m tonnes at 43.4%
MgO, 0.66% CaO, 0.76% Fe2O3, 0.26%
Al2O3, 0.11% SiO2 and 5.9%
Insolubles to approximately 45 metres depth.
The Huandot deposit is located
approximately 70km south of Darwin and is adjacent to sealed
roads, including the Stuart Highway and the Batchelor to Rum
Jungle Road, as well as the Darwin to Alice Springs railway
(Figure 1). It is also close to major infrastructure
such as high voltage power, gas and water.
The Huandot magnesite deposit was
first evaluated by BHP during 1979-1983 for refractory grade
material. Metallurgical work (by Grundstofftechnik Germany)
showed a low silica (0.8%) product suitable for refractory
grade could be made from the samples. It was subsequently
evaluated as a raw material for magnesium metal production by
Commercial Minerals Ltd. Based on a 26,000 tonne bulk sample
sent in 1995 to Norsk Hydro in Canada, the quality was
suggested to be comparable with Norsks required
specifications.
More recent investigation by
Thessally demonstrated that the raw material could be used as a
feedstock for production of caustic calcined magnesia (CCM) and
dead burned magnesia (DBM). Lab calcination testwork to date
concluded that: There is unlikely to be any major
impediment to using the crushed magnesite for CCM production,
or selling it in its raw state for most established
applications.
Thessally is presently
investigating market opportunities for the development of the
Huandot magnesite deposit. The company has compiled and
validated the historic data on the known resource and has
planned a work program to demonstrate the resource potential
and product quality, including process options to remove
silica.
Initial conceptual studies has
provided confidence that the location of the project, with
respect to key infrastructure and the shallow, continuous and
pure nature of the project, provide the opportunity to consider
a variety of development scenarios.
The mineralisation remains open at
depth and along strike and, assuming it extends to at least 90-
20 metres vertical depth, there may be a further 5-10m tonnes
magnesite as a potential exploration target immediately below
the current defined resource. This figure could rapidly be
increased when strike extensions are taken into account.


Magnesite definition and genesis
Magnesite is the mineral name for
MgCO3 with a theoretical MgO content of 47.8% MgO
and 52.2% CO2. Deposits of magnesite are of two main
types; (i) macrocrystalline or sparry rocks (Wilson, 2013)
where Mg solutions have altered dolomite to magnesite, and (ii)
cryptocrystalline magnesite replacing ultramafic rocks within
the weathered profile. Other types of magnesite, such as
sedimentary beds, crystalline magnesite replacement in
ultramafic rocks and saline brines, do occur but are of
secondary significance from an economic point of view. Also a
pure form of magnesia (MgO) is produced from sea water.
Crystalline magnesite formed from
Mg metasomatic replacement in dolomites can contain both
calcite and dolomite as impurities as well as silica, if chert
was present in the original dolomite. In cryptocrystalline
magnesite impurities are siliceous minerals such as serpentine
and quartz. Other impurities can include iron and manganese
oxides and silicates of Ca, Al, Mn and Fe.
As noted by Wilson (2013) the
quality of sparry-type magnesite may be improved by removing
silicate minerals during a flotation stage, while
cryptocrystalline magnesite can be upgraded by hand sorting or
more automated methods such as optical and magnetic
sorting.

Magnesite markets and producers
Magnesite loses CO2 when
heated above 800¡C with a firing range of 800¡C to
1000¡C, resulting in a caustic (ie. reactive) magnesia
(CCM) and a firing range of 1,450¡C to 1,600¡C,
resulting in a dead burned magnesia (DBM) in which the MgO
occurs as the periclase mineral phase. At very high
temperatures; i.e. 3,000¡C a fused form of magnesia (FM)
is produced.
The main commercial use of
magnesite is as DBM in refractories. CCM and FM are also
important markets, though secondary to DBM. In the form of raw
magnesite the mineral has a limited direct market, with soil
conditioning being one example.
Work to date by Thessally has
focussed on the production of CCM, but it is intended to
investigate the potential to process further to DBM.
In 2012 USGS data shows world
production capacity of CCM as 2.72m tonnes MgO and DBM as 7.64m
tonnes MgO (Bray, 2012). Australias share of this
production capacity in 2012 was 8% CCM and 1.4% DBM. China
dominates the supply of CCM with 53% of production capacity.
Russia (3.4%), Spain (5.5%), and Brazil and Canada (3.5%) are
other significant CCM producers, according to the USGS.
The production of CCM is mainly
based on the product being a precursor for DBM and FM. In the
form of CCM the product supplies a wide range of end users (34
being a number quoted at the IM MagMin
conference in June 2014) with agriculture and water treatment
being the main industrial markets. The bulk; ie. 90%; of CCM
product is based on natural magnesite with the remaining 10%
sourced from seawater and saline brines.
The largest market for CCM is
animal feed where magnesium is critical in dietary requirements
for cattle, sheep and other livestock. It is estimated that the
present worldwide consumption of CCM in animal feeds is about
470,000 tonnes but this is forecast to grow to about 600,000
tonnes by 2020, mainly due to changing dietary habits in Asian
countries.
The second key market for CCM is in
wastewater treatment where the product is a competitor material
to lime. Both materials serve the key purposes of
neutralisation and precipitation of heavy metals.
There are a number of positive
aspects to using CCM over lime; eg. in the case of neutralising
sulphuric acid waste streams the reaction with magnesia (in the
form of magnesium hydroxide) produces soluble magnesium
sulphate, while the reaction with lime produces slightly
soluble calcium sulphate which leads to blocking of resultant
filtercakes.
Other significant markets for CCM
are pulp and paper, fertilisers, iron and steelmaking and
hydrometallurgy. Minor uses are numerous and varied, including
as a vulcanising agent in rubber and as a viscosity agent in
drilling muds (Harben, 2002; Kramer, 2006).
At the IM MagMin
June 2014 conference, the point was made by a panel of experts
that, A lack of investment in research and development
for CCM is preventing the sector from realising opportunities
to expand the market. A number of reasons were put
forward for this including the low level of CCM industry
profitability, a perceived lack of patentable outcomes for
R&D and the use of CCM as a precursor for DBM.

Magnesite specifications and prices
As the main products from magnesite
mines are in the calcined MgO form, this is how the product
specifications are quoted. For CCM produced from natural
magnesite the range of MgO is 85-95%, with 85-90% MgO being the
typical range for animal feeds and fertilisers and 90-95% MgO
for bulk industrial applications such as construction and paper
processing.
The grades of DBM are also variable
with grades supplied from China (36% of world production
capacity - USGS 2012) quoted as 90%, 92%, 94-95% MgO (IM
July 2014). There is also a high grade of 97.5% MgO quoted
but it is likely that this is not sourced from a natural
magnesite.
The main Australian producer is
QMAG (Queensland Magnesia) which mines a cryptocrystalline
magnesite deposit. This company sets the benchmark for magnesia
in Australia and, as such, the company product specifications
are relevant (Table 1). Prices for DBM are available
without restrictions, but those for CCM are less so.

Deposit setting, geology and exploration
Magnesite was first noted in the
Coomalie Dolostone in 1968 at the Mount Fitch uranium deposit
and may be classified as macrocrystalline magnesite
which is typically formed when magnesia-rich fluids cause
alteration of limestone or dolomite.
Exploration for magnesite in the
late 1970s to early 1980s by Geopeko and BHP Exploration
indicated the presence of a significant magnesite resource.
This was followed in 1990-1993 when Nircon Resources/Aztec
Mining drilled over 1,700m across the magnesite deposits and
estimated a resource of 5.8m tonnes (Table 3).
In 1994 the Huandot (ERL128)
deposit was acquired by Normandy Mining Ltd, and its subsidiary
Normandy Industrial Minerals Ltd (NIML), who drilled 3,500m RC
and estimated a Mineral Resource of 4.6m tonnes at 43.4% MgO,
0.66% CaO, 0.76% Fe2O3, 0.26%
Al2O3, 0.11% SiO2 and 5.9%
Insolubles. Analyses (including 1996 re-analyses of the diamond
drill core) were by EDTA and/or an acid digest method supplied
by Norsk Hydro Canada Inc.
At Huandot, the magnesite occurs as
an elongate lens, 80-120 metres wide, along the western and
south-eastern limbs of a north east plunging syncline, referred
to locally as the Huandot syncline (Figure 3). The
most extensive magnesite zone (western zone) is >500 metres
long on the western limb, which dips east at about
50-60¡. A separate magnesite concentration (eastern zone)
occurs on the south-eastern limb, which dips to the
north-north-west at 40-50¡. The synclinal axis plunges to
the north-north-west at 40-60¡.
Karst weathering has created a very
irregular surface on the massive high-grade magnesite. This
weathering is more intense in the keel of the syncline between
the two deposits and extends to a depth of 40-50 metres (Lines,
2012). Depth to massive unweathered magnesite on the limbs of
the syncline varies from zero to approximately 20 metres
(Figure 4). Reasonably large solution cavities were encountered
within the massive magnesite during extraction of the bulk
sample and during subsequent drilling programmes.
NIML estimated the resource using
block modelling and an SG of 2.95 g/ml. NIMLs Mineral
Resource estimate is all within approximately 45 metres of the
surface. As highlighted in Figure 4, there is potential to
significantly extend the resource at depth and along
strike.

Laboratory testwork
A small 7kg sample of outcropping
magnesite was submitted to Grundstofftechnik Gmbh of Essen,
Germany, in 1980, and, according to flotation test results, it
was concluded that a low silica product could be produced for
the refractory industry.
During 1995 a 26,000 tonne bulk
sample was mined, screened to 90% passing -100mm + 10cm and
washed. Testwork by Norsk Hydro in Canada indicated that the
quality was generally comparable with the companys
SPEC-100 grade (Table 4).
Subsequently, during 2013,
Thessally had a number of pieces of magnesite from stockpiles
at the deposit tested for calcining properties. While not
necessarily representative of the entire resource, these
samples were expected to be indicative of the initial mine
product.
Visually, two crystalline groups
were chosen for assessment; (i) finer-grained sample
UK (Figure 5) and, ii) coarse-grained
sample #14. The samples were cut into blocks for calcination
tests which took place in a large static muffle furnace. The
small specimens of magnesite were photographed, measured,
weighed and heated from 200 oC to 875 oC
with a temperature rise profile of 7.5 ¡C per minute and
retention time similar to that which would be experienced in a
commercial kiln.
Key outcomes of the calcining tests
were: no significant decrepitation or spalling throughout the
calcination process, good dimensional stability, strength and
abrasion resistance, which indicated that a mix of these
magnesites would withstand a typical gas fired multiple hearth
furnace used for the production of CCM.
A petrographic thin section and SEM
study of sample UK during 2014 confirmed that it is
predominantly composed of magnesite (>95%) which forms a
medium grained (0.5-1 mm) interlocking mosaic of sub-rhombic
bladed crystals (Figure 6). Accessory minerals include
patches of magnesium chlorite, plus rare quartz. According to
SEM analysis the typical magnesite composition is 46.5% MgO,
0.9% CaO. 0.6% FeO, which is comparable with the whole rock XRF
analysis presented in Table 5.

Summary
Thessally Resources Huandot
deposit is located approximately 70km south of Darwin and is
close to major infrastructure such as sealed roads, the Darwin
to Alice Springs railway, high voltage power, gas and
water.
During 1995 a 26,000 tonne bulk
sample was mined, screened to 90% passing -100mm + 10cm and
washed. Testwork by Norsk Hydro in Canada indicated that the
quality was generally comparable with the companys
SPEC-100 grade.
Normandy Industrial Minerals Ltd
(NIML) estimated a Mineral Resource of 4.6Mt at 43.4% MgO. Lab
calcining tests in 2013 indicated that the magnesite could be
suitable for CCM production.
Thessally has compiled and
validated the historic data on the known resource and has
planned a work program to demonstrate the resource
potential.
The company is presently
investigating opportunities in natural magnesite, CCM and DBM
markets.
Acknowledgements
The management of Thessaly
Resources is sincerely thanked for access to the companys
database and for permission to publish this short report.
Authors
Andrew Scogings
(MAIG, MAusIMM) holds a PhD in geology and is a director of
KlipStone Pty Ltd
Rob Barnett
(FGSSA, Pr. Sci. Nat) holds a MSc in industrial mineralogy and
is an associate industrial minerals consultant at KlipStone Pty
Ltd
www.klipstone.com.au
References
Bray, E. L., 2012.
USGS 2012 Minerals Yearbook, Magnesium Compounds.
Harbin, P. W.,
2002. Magnesium Minerals and Compounds. The
Industrial Minerals Handybook. A Guide to Markets,
Specifications and Prices, 194-207.
Kramer, D. A.,
2006. Magnesium Minerals and Compounds. Industrial
Minerals & Rocks. Commodities, Markets, and Uses.
7th Edition, 615-629.
Lines, M., 2012.
Review of Preliminary Economic Assessment Parameters.
Huandot Magnesite Deposit, Batchelor, Northern
Territory.
Wilson, I., 2013. Global update on
magnesite resources and production. Industrial Minerals
Magazine, September 2013.